void tpDestroy(ThreadPool *tp, int shouldWaitForTasks) {
if(sem_trywait(&(tp->sem_tpDestroyWasInvoked))){//we are already during destruction
return;
}
tp->tpDestroyNeedsLock = 1;
if (pthread_mutex_lock(&(tp->mutex_taskQueue_lock))) {//ERROORRRREE
return;//TODO think about this
}
if(shouldWaitForTasks==0){
while(!(osIsQueueEmpty(tp->taskQueue))){
free(osDequeue(tp->taskQueue));
}
}
int i;
for(i = 0 ; i < tp->numOfThreads ; ++i){
FuncAndParam* fap = malloc(sizeof(*fap));
fap->function = selfDestruct;
fap->param = NULL;
osEnqueue(tp->taskQueue, (void*)fap);
}
tp->tpDestroyNeedsLock = 0;
if (pthread_cond_broadcast(&(tp->cond_taskQueueNotEmpty))) {//ERROORRRREE
return;
}
if (pthread_mutex_unlock(&(tp->mutex_taskQueue_lock))) {//ERROORRRREE
return;
}
int elDestroyador = getpid();//id of the process that invoked tpDestroy
int flagCurrentIsThread = 0;//true iff the process that invoked tpDestroy is one of the threads
for(i = 0 ; i < tp->numOfThreads ; ++i){
if((tp->threadIdArray)[i]==elDestroyador){
flagCurrentIsThread = 1;
}else{
pthread_join((tp->threadIdArray)[i], NULL);
}
}
while(!(osIsQueueEmpty(tp->taskQueue))){
free(osDequeue(tp->taskQueue));
}
osDestroyQueue(tp->taskQueue);
if (pthread_cond_destroy(&(tp->cond_taskQueueNotEmpty))) {//ERROORRRREE
return;
}
if (pthread_mutex_destroy(&(tp->mutex_taskQueue_lock))) {//ERROORRRREE
return;
}
if (sem_destroy(&(tp->sem_tpDestroyWasInvoked))) {//ERROORRRREE
return;
}
free(tp->threadIdArray);
free(tp);
if(flagCurrentIsThread){//if the process that invoked tpDestroy is one of the threads
pthread_exit(NULL);
}
}
/**
* Destroys the thread pool.
*
* 1. Lock the destruction lock (top priority... don't want to starve here)
* 2. Change the state
* 3. Unlock the destruction lock (now, no more tasks can be added because the state
* is checked first, and the threads should know to check the state before dequeuing
* anything)
* 4. Lock the tasks lock, so we're sure all threads are waiting for a signal (or for
* the lock) to prevent deadlock (see comments bellow).
* 5. Broadcast to all threads waiting for tasks: if there's nothing now, there never
* will be!
* 6. Unlock the tasks lock (to allow the threads to do their thing)
* 7. Wait for all threads to finish
* 8. Destroy all fields of the pool
*/
void tpDestroy(ThreadPool* tp, int should_wait_for_tasks) {
if (!tp) // Sanity check
return;
if (!start_write(tp)) { // Someone is already writing to pool->state!
return; // This should only happen ONCE...
}
if (tp->state != ALIVE) { // Destruction already in progress.
end_write(tp); // This can happen if destroy() is called twice fast
return;
}
tp->state = should_wait_for_tasks ? DO_ALL : DO_RUN; // Enter destroy mode
PRINT("Destroying the pool! Now allowing state read.\n");
end_write(tp); // Allow reading the state
// Make sure the queue isn't busy.
// We shouldn't encounter deadlock/livelock here because threads wait for signals, and the only
// possible source of a signal is here or in tpInsertTask().
// If we lock this only AFTER we change the/ destruction state, we can create a situation where
// a thread waits forever for a signal that will never come:
// - A thread is in it's while loop, the queue is
// empty and the pool isn't being destroyed
// so it enters the body of the loop. Before it
// starts waiting for a signal...
// - CS-->Main thread
// - Main thread calls destroy, doesn't wait for
// the task_lock and writes the new destruction
// state. Then, broadcasts a signal to listening
// threads.
// - CS-->Previous thread
// - Starts waiting for a signal that will never
// come
// By locking here before broadcasting the destruction, we make sure all threads are waiting for
// the lock or for the signal! Either way, after the signal, the threads will know what to do and
// exit the loop.
pthread_mutex_lock(&tp->task_lock);
PRINT("Pool destroyed, task lock locked, sending broadcast...\n");
pthread_cond_broadcast(&tp->queue_not_empty_or_dying);
PRINT("... done. Unlocking the task lock.\n");
pthread_mutex_unlock(&tp->task_lock);
// Wait for all threads to exit (this could take a while)
int i;
for (i=0; i<tp->N; ++i) {
#if HW3_DEBUG
PRINT("Waiting for T%2d to finish (tid=%d)...\n", i+1, tp->tids[i]);
#else
PRINT("Waiting for thread %d to finish...\n", i+1);
#endif
pthread_join(tp->threads[i], NULL);
#if HW3_DEBUG
PRINT("T%2d (tid=%d) done.\n", i+1, tp->tids[i]);
#else
PRINT("Thread %d done.\n", i+1);
#endif
}
PRINT("All threads done! Locking the task lock and destroying the task queue...\n");
// Cleanup!
// Tasks (we can still lock here):
pthread_mutex_lock(&tp->task_lock);
while (!osIsQueueEmpty(tp->tasks)) {
Task* t = (Task*)osDequeue(tp->tasks);
free(t);
}
osDestroyQueue(tp->tasks);
PRINT("Done. Unlocking the task queue\n");
pthread_mutex_unlock(&tp->task_lock);
// Locks:
PRINT("Doing thread pool cleanup...\n");
pthread_mutex_destroy(&tp->task_lock);
pthread_mutexattr_destroy(&tp->mutex_type);
sem_destroy(&tp->r_num_mutex);
sem_destroy(&tp->w_flag_mutex);
sem_destroy(&tp->r_entry);
sem_destroy(&tp->r_try);
sem_destroy(&tp->state_lock);
pthread_cond_destroy(&tp->queue_not_empty_or_dying);
// Last cleanup, and out:
#if HW3_DEBUG
free(tp->tids);
#endif
free(tp->threads);
free(tp);
PRINT("Done destroying thread pool.\n");
return;
}
